Method of improving light stability of flexographic printing plates featuring flat top dots

ABSTRACT

A photocurable relief image printing blank comprising: (a) a support layer; (b) one or more photocurable layers disposed on the support layer, wherein the one or more photocurable layers comprise: i) a binder; ii) one or more monomers; iii) a photoinitiator; iv) an additive selected from the group consisting of phosphites, phosphines, thioether amine compounds, and combinations of one or more of the foregoing; and v) an additional component comprising amine moieties; (c) a laser ablatable masking layer disposed on the one or more photocurable layers, the laser ablatable masking layer comprising a radiation opaque material; and (d) optionally, a removable coversheet. Upon exposure and development, the resulting relief image printing element does not degrade if left under ambient UV lights for an extended period of time.

FIELD OF THE INVENTION

The present invention relates generally to a digital relief imageprinting elements having improved storage stability.

BACKGROUND OF THE INVENTION

Flexography is a method of printing that is commonly used forhigh-volume runs. Flexography is employed for printing on a variety ofsubstrates such as paper, paperboard stock, corrugated board, films,foils and laminates. Newspapers and grocery bags are prominent examples.Coarse surfaces and stretch films can be economically printed only bymeans of flexography.

Flexographic printing plates are relief plates with image elementsraised above open areas. Generally, the plate is somewhat soft, andflexible enough to wrap around a printing cylinder, and durable enoughto print over a million copies. Such plates offer a number of advantagesto the printer, based chiefly on their durability and the ease withwhich they can be made. A typical flexographic printing plate asdelivered by its manufacturer is a multilayered article made of, inorder, a backing or support layer; one or more unexposed photocurablelayers; optionally a protective layer or slip film; and often, aprotective cover sheet.

The support (or backing) layer lends support to the plate. The supportlayer can be formed from a transparent or opaque material such as paper,cellulose film, plastic, or metal. Preferred materials include sheetsmade from synthetic polymeric materials such as polyesters, polystyrene,polyolefins, polyamides, and the like. One widely used support layer isa flexible film of polyethylene terephthalate.

The photocurable layer(s) can include any of the known polymers,monomers, initiators, reactive and/or non-reactive diluents, fillers,and dyes. As used herein, the term “photocurable” refers to acomposition which undergoes polymerization, cross-linking, or any othercuring or hardening reaction in response to actinic radiation with theresult that the unexposed portions of the material can be selectivelyseparated and removed from the exposed (cured) portions to form athree-dimensional relief pattern of cured material. Exemplaryphotocurable materials are disclosed in European Patent Application Nos.0 456 336 A2 and 0 640 878 A1 to Goss, et al., British Patent No.1,366,769, U.S. Pat. No. 5,223,375 to Berrier, et al., U.S. Pat. No.3,867,153 to MacLahan, U.S. Pat. No. 4,264,705 to Allen, U.S. Pat. Nos.4,323,636, 4,323,637, 4,369,246, and 4,423,135 all to Chen, et al., U.S.Pat. No. 3,265,765 to Holden, et al., U.S. Pat. No. 4,320,188 to Heinz,et al., U.S. Pat. No. 4,427,759 to Gruetzmacher, et al., U.S. Pat. No.4,622,088 to Min, and U.S. Pat. No. 5,135,827 to Bohm, et al., thesubject matter of each of which is herein incorporated by reference inits entirety. More than one photocurable layer may also be used.

Photocurable materials generally cross-link (cure) and harden throughradical polymerization in at least some actinic wavelength region. Asused herein, “actinic radiation” refers to radiation that is capable ofpolymerizing, crosslinking or curing the photocurable layer. Actinicradiation includes, for example, amplified (e.g., laser) andnon-amplified light, particularly in the ultraviolet (UV) and violetwavelength regions.

The slip film is a thin layer, which protects the photopolymer from dustand increases its ease of handling. In a conventional (“analog”) platemaking process, the slip film is transparent to UV light, and theprinter peels the cover sheet off the printing plate blank, and places anegative on top of the slip film layer. The plate and negative are thensubjected to flood-exposure by UV light through the negative. The areasexposed to the light cure, or harden, and the unexposed areas areremoved (developed) to create the relief image on the printing plate.

In a “digital” or “direct to plate” process, a laser is guided by animage stored in an electronic data file, and is used to create an insitu negative in a digital (i.e., laser ablatable) masking layer, whichis generally a slip film which has been modified to include a radiationopaque material. Portions of the laser ablatable layer are then ablatedby exposing the masking layer to laser radiation at a selectedwavelength and power of the laser. Examples of laser ablatable layersare disclosed, for example, in U.S. Pat. No. 5,925,500 to Yang, et al.,and U.S. Pat. Nos. 5,262,275 and 6,238,837 to Fan, the subject matter ofeach of which is herein incorporated by reference in its entirety.

Processing steps for forming relief image printing elements typicallyinclude the following:

-   -   1) Image generation, which may be mask ablation for digital        “computer to plate” printing plates or negative production for        conventional analog plates;    -   2) Back exposure to create a floor layer in the photocurable        layer and establish the depth of relief;    -   3) Face exposure through the mask (or negative) to selectively        crosslink and cure portions of the photocurable layer not        covered by the mask, thereby creating the relief image;    -   4) Development to remove unexposed photopolymer by solvent        (including water) or thermal development; and    -   5) If necessary, post exposure and detackification.

Removable coversheets are also preferably provided to protect thephotocurable printing element from damage during transport and handling.Prior to processing the printing elements, the coversheet is removed andthe photosensitive surface is exposed to actinic radiation in animagewise fashion. Upon imagewise exposure to actinic radiation,polymerization, and hence, insolubilization of the photopolymerizablelayer occurs in the exposed areas. Treatment with a suitable developersolvent (or alternatively, thermal development) removes the unexposedareas of the photopolymerizable layer, leaving behind a printing reliefthat can be used for flexographic printing.

As used herein “back exposure” refers to a blanket exposure to actinicradiation of the photopolymerizable layer on the side opposite thatwhich does, or ultimately will, bear the relief. This step is typicallyaccomplished through a transparent support layer and is used to create ashallow layer of photocured material, i.e., the “floor,” on the supportside of the photocurable layer. The purpose of the floor is generally tosensitize the photocurable layer and to establish the depth of relief.

Following the brief back exposure step (i.e., brief as compared to theimagewise exposure step which follows), an imagewise exposure isperformed utilizing a digitally-imaged mask or a photographic negativemask, which is in contact with the photocurable layer and through whichactinic radiation is directed.

The type of radiation used is dependent on the type of photoinitiator inthe photopolymerizable layer. The digitally-imaged mask or photographicnegative prevents the material beneath from being exposed to the actinicradiation and hence those areas covered by the mask do not polymerize,while the areas not covered by the mask are exposed to actinic radiationand polymerize. Any conventional sources of actinic radiation can beused for this exposure step, including, for example, carbon arcs,mercury-vapor arcs, fluorescent lamps, electron flash units, electronbeam units, LEDs and photographic flood lamps.

After imaging, the photosensitive printing element is developed toremove the unpolymerized portions of the layer of photocurable materialand reveal the crosslinked relief image in the cured photosensitiveprinting element. Typical methods of development include washing withvarious solvents or water, often with a brush. Other possibilities fordevelopment include the use of an air knife or thermal development,which typically uses heat plus a blotting material. The resultingsurface has a relief pattern, which typically comprises a plurality ofdots that reproduces the image to be printed. After the relief image isdeveloped, the resulting relief image printing element may be mounted ona press and printing commenced. In addition, if necessary, after thedevelopment step, the relief image printing element may be post exposedand/or detackified as is generally well known in the art.

The shape of the dots and the depth of the relief, among other factors,affect the quality of the printed image. It is also very difficult toprint small graphic elements such as fine dots, lines and even textusing flexographic printing plates, while at the same time maintainingopen reverse text and shadows. In the lightest areas of the image(commonly referred to as highlights) the density of the image isrepresented by the total area of dots in a halftone screenrepresentation of a continuous tone image. For Amplitude Modulated (AM)screening, this involves shrinking a plurality of halftone dots locatedon a fixed periodic grid to a very small size, the density of thehighlight being represented by the area of the dots. For FrequencyModulated (FM) screening, the size of the halftone dots is generallymaintained at some fixed value, and the number of randomly orpseudo-randomly placed dots represent the density of the image. In bothcases, it is necessary to print very small dot sizes to adequatelyrepresent the highlight areas.

Bullet shaped round top dots (RTDs) are created in conventional digitalplates, and are attributed to oxygen inhibition taking place on thesurface layer during the imaging process. It has been demonstrated thatflat top dots (FTDs) are superior to RTDs in printing performance.However, in order to obtain FIDs, oxygen inhibition in the surface layermust be suppressed.

In addition, maintaining small dots on flexographic plates can be verydifficult due to the nature of the platemaking process. In digitalplatemaking processes that use a UV-opaque mask layer, the combinationof the mask and UV exposure produces relief dots that have a generallyconical shape. The smallest of these dots are prone to being removedduring processing, which means no ink is transferred to these areasduring printing (i.e., the dot is not “held” on plate and/or on press).Alternatively, if the dots survive processing they are susceptible todamage on press. For example small dots can fold over and/or partiallybreak off during printing, causing either excess ink or no ink to betransferred.

As described in U.S. Pat. No. 8,158,331 to Recchia and U.S. Pat. Pub.No. 2011/0079158 to Recchia et al., the subject matter of each of whichis herein incorporated by reference in its entirety, a particular set ofgeometric characteristics can define a flexo dot shape that yieldssuperior printing performance, including but not limited to (1)planarity of the dot surface; (2) shoulder angle of the dot; (3) depthof relief between the dots; and (4) sharpness of the edge at the pointwhere the dot top transitions to the dot shoulder.

In order to improve surface cure, it has also generally been found thatit is beneficial to perform additional procedures and/or use additionalequipment, including: (1) laminating a membrane onto the surface of thephotopolymer; (2) purging oxygen from the photopolymer using an inertgas; and/or (3) imaging the photopolymer with a high intensity UVsource.

Purging oxygen from the photopolymer using an inert gas typicallyinvolves placing the photocurable resin plate in an atmosphere of inertgas, such as carbon dioxide gas or nitrogen gas, before exposure, inorder to displace the environmental oxygen. A noted drawback to thismethod is that it is inconvenient and cumbersome and requires a largespace for the apparatus.

Another approach involves subjecting the plates to a preliminaryexposure (i.e., “bump exposure”) of actinic radiation. During bumpexposure, a low intensity “pre-exposure” dose of actinic radiation isused to sensitize the resin before the plate is subjected to the higherintensity main exposure dose of actinic radiation. The bump exposure istypically applied to the entire plate area and is a short, low doseexposure of the plate that reduces the concentration of oxygen, whichinhibits photopolymerization of the plate (or other printing element)and aids in preserving fine features (i.e., highlight dots, fine lines,isolated dots, etc.) on the finished plate. However, thepre-sensitization step can also cause shadow tones to fill in, therebyreducing the tonal range of the halftones in the image. In thealternative, a selective preliminary exposure, as discussed for examplein U.S. Patent Publication No. 2009/0043138 to Roberts et al., thesubject matter of which is herein incorporated by reference in itsentirety, has also been proposed.

Other efforts to reduce the effects of oxygen on the photopolymerizationprocess have been directed to the use of special plate formulationsalone or in combination with the bump exposure. For example,flexographic printing plates have been developed to inherently renderFTDs without resorting to the above mentioned methods. These inherent HDplates greatly streamline plate-making procedures and save costsrequired to support the additional equipment and techniques asdescribed, for example in U.S. Pat. No. 8,808,968 to Choi et al., thesubject matter of which is herein incorporated by reference in itsentirety. These photocurable relief image printing elements comprise: anadditive selected from the group consisting of phosphites, phosphines,thioether amine compounds, and combinations of one or more of theforegoing in the photocurable layer.

However, fully-processed inherent FTD plates such as those described inU.S. Pat. No. 8,808,968, tend to have light instability due to theirunique nature of photoresin chemistries. As a result, these FTDphotoresins have a tendency to degrade if left under ambient UV lights(˜0.4 μW/cm²) for an extended period of time (i.e., greater than 2weeks) even in a climate-controlled environment. The degradedphotoresins become brittle and lose resilience, which greatly comprisesprinting performance. If the degradation continues, cracks are createdin the bulk photoresin upon stress, as seen in FIG. 1. Therefore, theseinherent FTD plates need to be kept covered or stored in a darkenvironment to prevent ambient UV light from degrading the plates.

Thus, it would be desirable to provide an improved photocurablecomposition for use as fully processed inherent FTD plates and thatexhibits good light stability and does not degrade, even after beingstored for an extended period of time.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a relief imageprinting element having improved surface cure.

It is another object of the present invention to provide a method oftailoring or modifying the shape of relief printing dots in a reliefimage printing element for optimal printing on various substrates and/orunder various conditions.

It is still another object of the present invention to provide animproved method of producing relief image printing elements comprisingdots having desirable geometric characteristics.

It is still another object of the present invention to streamline theworkflow of a digital platemaking process.

It is still another object of the present invention to provide animproved method of creating a relief image printing element havingtailored relief dots in terms of edge definition, should angle and/orprint surface.

It is still another object of the present invention to provide aphotocurable composition for use as a fully processed inherent FTDplate.

It is still another object of the present invention to provide aphotocurable composition that exhibits good light stability.

It is yet another object of the present invention to provide aphotocurable composition that does not degrade, even after being storedfor an extended period of time.

To that end, in one embodiment, the present invention relates generallyto a photocurable relief image printing element comprising:

-   -   a) a support layer;    -   b) one or more photocurable layers disposed on the support        layer, wherein the one or more photocurable layers comprise:        -   i) a binder;        -   ii) one or more monomers;        -   iii) a photoinitiator;        -   iv) an additive selected from the group consisting of            phosphites, phosphines, thioether amine compounds, and            combinations of one or more of the foregoing; and        -   v) an additional component comprising amine moieties;    -   c) a laser ablatable masking layer disposed on the one or more        photocurable layers, the laser ablatable masking layer        comprising a radiation opaque material; and    -   d) optionally, a removable coversheet.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts cracks induced by ambient lights in an inherent FTDplate.

FIG. 2 depicts SEM pictures of 200 lpi dots in two different plateformulations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to an improved photocurablecomposition that improves light stability of fully-processed inherentFTD photoresins without resorting to conventional antioxidants that tendto compromise imaging features. The benefit of the improved photocurablecomposition of the present invention is comparable plate-handling andstorage characteristics of inherent FTD plates to those of conventionalplate formulations without compromising the technical superiority of theinherent FTD photoresins.

Due to the unique nature of the inherent FTD photoresins, fullyprocessed plates tend to exhibit poor light stability. As a result, theinherent FTD plates typically require stricter plate-handling protocolsfor storage in order to fully realize the technical benefits of inherentFTD plates. The inventors of the present invention have discovered thatthe use of a component comprising amine moieties in the photocurablecomposition can improve light stability of the plate withoutdeteriorating imaging features of inherent FTD photoresins.

As described herein, the purpose of the present invention is to improvelight stability of fully-processed inherent FTD plates without resortingto conventional antioxidants that tend to compromise distinct imagingfeatures of inherent FTD resins such as 1:1 reproduction (dot size onfile≈dot size on plate) and well-defined flat top dots. The presentinvention relates generally to an improved photopolymer composition thatcontains an additional component containing amine entities in variousmaterials, such as photoinitiators, HALs, metals salts, amine acrylates,and amines.

In one embodiment, the present invention relates generally to aphotocurable relief image printing element comprising:

-   -   a) a support layer;    -   b) one or more photocurable layers disposed on the support        layer, wherein the one or more photocurable layers comprise:        -   i) a binder;        -   ii) one or more monomers;        -   iii) a photoinitiator;        -   iv) an additive selected from the group consisting of            phosphites, phosphines, thioether amine compounds, and            combinations of one or more of the foregoing; and        -   v) an additional component comprising amine moieties;    -   c) a laser ablatable masking layer disposed on the one or more        photocurable layers, the laser ablatable masking layer        comprising a radiation opaque material; and    -   d) optionally, a removable coversheet.

The photopolymerizable composition generally comprises one or morebinders, monomers and plasticizers in combination with one or morephoto-initiators and the above-described additives.

The binder type is not critical to the photopolymer composition andmost, if not all, styrenic copolymer rubbers are usable in thecompositions of the invention. Suitable binders include natural orsynthetic polymers of conjugated diolefin hydrocarbons, including1,2-polybutadiene, 1,4-polybutadiene, butadiene/acrylonitrile,butadiene/styrene, thermoplastic-elastomeric block copolymers e.g.,styrene-butadiene-styrene block copolymer, styrene-isoprene-styreneblock copolymer, etc., and copolymers of the binders. It is generallypreferred that the binder be present in at least an amount of 60% byweight of the photosensitive layer. The term binder, as used herein,also encompasses core shell microgels or blends of microgels andpre-formed macromolecular polymers.

Non-limiting examples of binders that are usable in the compositions ofthe instant invention include styrene isoprene styrene (SIS), acommercial product of which is available from Kraton Polymers, LLC underthe tradename Kraton® D1161; styrene isoprene butadiene styrene (SIBS),a commercial product of which is available from Kraton Polymers, LLCunder the tradename Kraton® D1171; and styrene butadiene styrene (SBS),a commercial product of which is available from Kraton Polymers LLCunder the tradename Kraton® DX405.

Monomers suitable for use in the present invention areaddition-polymerizable ethylenically unsaturated compounds. Thephotocurable composition may contain a single monomer or a mixture ofmonomers which form compatible mixtures with the binder(s) to produceclear (i.e., non-cloudy) photosensitive layers. The monomers aretypically reactive monomers especially acrylates and methacrylates. Suchreactive monomers include, but are not limited to, trimethylolpropanetriacrylate, hexanediol diacrylate, 1,3-butylene glycol diacrylate,diethylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentylglycol diacrylate, polyethylene glycol-200 diacrylate, tetraethyleneglycol diacrylate, triethylene glycol diacrylate, pentaerythritoltetraacrylate, tripropylene glycol diacrylate, ethoxylated bisphenol-Adiacrylate, trimethylolpropane triacrylate, di-imethylolpropanetetraacrylate, triacrylate of tris(hydroxyethyl)isocyanurate,dipentaerythritol hydroxypentaacrylate, pentaerythritol triacrylate,ethoxylated trimethylolpropane triacrylate, triethylene glycoldimethacrylate, ethylene glycol dimethacrylate, tetraethylene glycoldimethacrylate, polyethylene glycol-200 dimethacrylate, 1,6-hexanedioldimethacrylate, neopentyl glycol dimethacrylate, polyethylene glycol-600dimethacrylate, 1,3-butylene glycol dimethacrylate, ethoxylatedbisphenol-A dimethacrylate, trimethylolpropane trimethacrylate,diethylene glycol dimethacrylate. 1,4-butanediol diacrylate, diethyleneglycol dimethacrylate, pentaerythritol tetramethacrylate, glycerindimethacrylate, trimethylolpropane di methacrylate, pentaerythritoltrimethacrylate, pentaerythritol dimethacrylate, pentaerythritoldiacrylate, urethanemethacrylate or acrylate oligomers and the likewhich can be added to the photopolymerizable composition to modify thecured product. Monoacrylates including, for example, cyclohexylacrylate, isobornyl acrylate, lauryl acrylate and tetrahydrofurfurylacrylate and the corresponding methacrylates are also usable in thepractice of the invention. Especially preferred acrylate monomersinclude hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate(TMPTA). Especially preferred methacrylate monomers include hexanedioldimethacrylate (HDDMA) and triemethylolpropane trimethacrylate (TMPTA).It is generally preferred that the one or more monomers be present in atleast an amount of 5% by weight of the photosensitive layer.

The photopolymer layer also optionally, but preferably, contains acompatible plasticizer, which serves to lower the glass transitiontemperature of the binder and facilitate selective development. Suitableplasticizers include, but are not limited to, dialkyl phthalates, alkylphosphates, polyethylene glycol, polyethylene glycol esters,polyethylene glycol ethers, polybutadiene, polybutadiene styrenecopolymers, hydrogenated, heavy naphthenic oils, hydrogenated, heavyparaffinic oils, and polyisoprenes. Other useful plasticizers includeoleic acid, lauric acid, etc. If used, the plasticizer is generallypresent in an amount of at least 10% by weight, based on weight of totalsolids of the photopolymer composition. Commercially availableplasticizers for use in compositions of the invention include1,2-polybutadiene, available from Nippon Soda Co. under the tradenameNisso PB B-1000; Ricon 183, which is a polybutadiene styrene copolymer,available from Cray Valley; Nyflex 222B, which is a hydrogenated heavynaphthenic oil, available from Nynas AB; ParaLux 2401, which is ahydrogenated heavy paraffinic oil, available from Chevron U.S.A., Inc.;and Isolene 40-S, which is a polyisoprene available from RoyalElastomers.

Photoinitiators for the photocurable composition include benzoin alkylethers, such as benzoin methyl ether, benzoin ethyl ether, benzoinisopropyl ether and benzoin isobutyl ether. Another class ofphotoinitiators are the dialkoxyacetophenones such as2,2-dimethoxy-2-phenylacetophenone and2,2-diethoxy-2-phenylacetophenone. Still another class ofphotoinitiators are the aldehyde and ketone carbonyl compounds having atleast one aromatic nucleus attached directly to the carboxyl group.These photoinitiators include, but are not limited to, benzophenone,acetophenone, o-methoxybenzophenone, acenaphthenequinone, methyl ethylketone, valerophenone, hexanophenone, alpha-phenylbutyrophenone,p-morpholinopropiophenone, dibenzosuberone, 4-morpholinobenzophenone,4′-morpholinodeoxybenzoin, p-diacetylbenzene, 4-aminobenzophenone,4′-methoxyacetopherione, benzaldehyde, alpha-tetralone,9-acetylphenarithrene, 2-acetylphenanthrene, 10-thioxanthenone,3-acetylphenanthrene, 3-acetylindone, 9-fluorenone, 1-indanone,1,3,5-triacetylbenzene, thioxanthen-9-one, xanthene-9-one,7-H-benz[de]-anthracene-7-one, 1-naphthaldehyde,4,4.degree.-bis(dimethylamino)-benzophenone, fluorene-9-one,1′-acetonaphthone, 2′-acetonaphthone, 2,3-butanedione, acetonaphthene,benz[a]anthracene 7.12 dione, etc. Phosphines such as triphenylphosphineand tri-otolylphosphine can also be used as photoinitiators.

Preferred photoinitiators for use in the photopolymer compositions ofthe invention include 2,2-dimethoxy-2-phenylacetophenone, a commercialproduct of which is available from BASF under the Tradename Irgacure®651; α-hydroxyketone, a commercial product of which is available fromBASF under the tradename Irgacure® 184; and acyl phosphine, a commercialproduct of which is available from Ciba Specialty Chemicals under thetradename Darocur® TPO. In one embodiment, it was determined thatIrgacure® 651 was the most effective photoinitiator for UV light withthe wavelength of ˜365 nm to obtain the benefits described herein.However, other photoinitiators can also be used, alone or in combinationwith Irgacure® 651.

As described herein, the additives may comprise phosphites, having thegeneral structure P(OR)₃ or P(OAr)₃, phosphines, having the generalstructure PR₃ or PAr₃, thioether amine compounds, or combinations of oneor more of the foregoing. The additive(s) may be used in thephotopolymer composition in an amount of about 0.1 to about 10% byweight, more preferably in an amount of about 0.05 to about 2% byweight.

Suitable phosphites include, but are not limited to,tris(nonylphenyl)phosphite (TNPP) (CAS No. 26523-78-4), triphenylphosphite, diphenyl phosphite, tridecyl phosphite, triisodecylphosphite, tris(tridecyl)phosphite, trilauryl phosphite, disterarylpentaerythriol diphosphite, diisodecyl phenyl phosphite, diphenylisodecyl phosphite, diphenyl octyl phosphite, diphenyl isooctylphosphite, diphenyl tri isodecyl monophenyl dipropyleneglycoldiphosphite, alkyl bisphenol A phosphite, tetraphenyl dipropyleneglycoldiphosphite, poly(dipropyleneglycol) phenyl phosphite, tris(dipropyleneglycol) phosphite, and dioleyl hydrogen phosphate. In one embodiment,the phosphite comprises TNPP.

Suitable phosphines include, but are not limited to, triphenylphosphine, tri-p-tolylphosphine, diphenylmethylphosphine,diphenylethylphosphine, diphenylpropylphosphine,dimethylphenylphosphine, diethylphenylphosphine,dipropylphenylphosphine, divinylphenylphosphine,divinyl-p-methoxyphenylphosphine, divinyl-p-bromophenylphosphine,divinyl-p-tolylphosphine, diallylphenylphosphine,divinyl-p-bromophenylphosphine, and diallyl-p-tolylphosphine.

Suitable thioether amine compounds include, but are not limited to,2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol(CAS No. 991-84-4),4-[[4,6-bis(nonylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(octadecylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-octylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-bis(2-methylnonan-2-yl)phenol,4-[[4,6-bis(hexylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(heptylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-y]amino]-2-tert-butyl-6-methylphenol,[4,6-bis(ethylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(2,4,4-trimethylpentan-2-ylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(2-octylsulfanylethylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-dibutylphenol,[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-dimethylphenol,2,6-ditert-butyl-4-[[4-(3,5-ditert-butyl-4-hydroxyanilino)-6-octylsulfany-1-1,3,5-triazin-2-yl]amino]phenol,4-[[4,6-bis(pentylsulfanyl)-1,3,5-triazin-2-yl]amino-2,6-dimethylphenol,4-[[4,6-bis(hexylsulfanyl)-1,3,5-triazin-2-yl]amino]-2-tert-butylphenol,2,6-ditert-butyl-4-[(4-octylsulfanyl-1,3,5-triazin-2-yl)amino]phenol,4-[[4,6-bis(ethylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-dimethylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl]-butylamino]-2,6-ditert-butylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl]-cyclohexylamino]-2,6-ditert-butylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl]amino]-6-tert-butylphenol,2-tert-butyl-6-methyl-4-[[4-octylsulfanyl-6-[(2,2,6,6,-tetramethylpiperid-in-4-yl)amino]-1,3,5-triazin-2-yl]amino]phenol,4-[[4,6-bis(octylsulfanylmethyl)-1,3,5-triazin-2-y]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl)methylamino]-2,6-di-tert-butylphenol,4-[(4-amino-6-chloro-1,3,5-triazin-2-yl)amino]-2,6-ditert-butylphenol,and4-[(4-cyclohexyl-6-cyclohexylsulfanyl-1,3,5-triazin-2-yl)amino]-2,6-d-i(propan-2-yl)phenol.In one embodiment, the thioether amine compound comprises2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol(also referred to as phenol,4-[[4,6-bis(octylthio)-1,3,5-triazin-2-yl]amino]-2,6-bis(1,1-dimethylethyl).

Various dyes and/or colorants may also optionally be used in thepractice of the invention although the inclusion of a dye and/orcolorant is not necessary to attain the benefits of the presentinvention. Suitable colorants are designated “window dyes” which do notabsorb actinic radiation in the region of the spectrum that theinitiator present in the composition is activatable. The colorantsinclude, for example, CI 109 Red dye, Methylene Violet (CI Basic Violet5), “Luxol.” Fast Blue MBSN (CI Solvent Blue 38), “Pontacyl” Wool BlueBL (CI Acid Blue 59 or CI 50315), “Pontacyl” Wool Blue GL (CI Acid Blue102 or CI 50320), Victoria Pure Blue BO (CI Basic Blue 7 or CI 42595),Rhodamine 3 GO (CI Basic Red 4), Rhodamine 6 GDN (CI Basic Red I or CI45160), 1,1′-diethyl-2,2′-cyanine iodide, Fuchsine dye (CI 42510),Calcocid Green S (CI 44090), Anthraquinone Blue 2 GA (CI Acid Blue 58),Solvaperm Red BB (Solvent Red 195), etc. The dyes and/or colorants mustnot interfere with the imagewise exposure.

Other additives including antiozonants, fillers or reinforcing agents,thermal polymerization inhibitors, UV absorbers, etc. may also beincluded in the photopolymerizable composition, depending on the finalproperties desired. Such additives are generally well known in the art.However, care must be taken to ensure that the use of these otheradditives do not compromise imaging properties of the photopolymerizablecomposition.

Suitable fillers and/or reinforcing agents include immiscible, polymericor nonpolymeric organic or inorganic fillers or reinforcing agents whichare essentially transparent at the wavelengths used for exposure of thephotopolymer material and which do not scatter actinic radiation, e.g.,polystyrene, the organophilic silicas, bentonites, silica, powderedglass, colloidal carbon, as well as various types of dyes and pigments.Such materials are used in amounts varying with the desired propertiesof the elastomeric compositions. The fillers are useful in improving thestrength of the elastomeric layer, reducing tack and, in addition, ascoloring agents.

Thermal polymerization inhibitors include, for example, p-methoxyphenol,hydroquinone, and alkyl and aryl-substituted hydroquinones and quinones,tert-butyl catechol, pyrogallol, copper resinate, naphthalamines,beta-naphthol, cuprous chloride, 2,6-di-tert-butyl-p-cresol, butylatedhydroxytoluene (BHT), oxalic acid, phenothiazine, pyridine, nitrobenzeneand dinitrobenzene, p-toluquinone and chloranil. While in some instancesit may be desirable to include a thermal polymerization inhibitor suchas BHT or similar thermal polymerization inhibitors in thephotopolymerizable composition, care must be taken to use BHT and othersimilar thermal polymerization inhibitors only in an amount and with acombination of other additives such that it does not comprise theimaging properties of the photopolymerizable resin, especially afterbeing stored for an extended period of time. Thus, in some instances, itis desirable that the photopolymerizable composition does not containany BHT and therefore is free of, or essentially free of BHT and othersimilar thermal polymerization inhibitors. In other instances, anddepending on the particular additional component containing aminemoieties being added, the photopolymerizable composition contains lessthan about 0.5 percent by weight, more preferably less than 0.1 percentby weight of BHT or similar thermal polymerization inhibitor.

As described herein, in order to improve the storage stability of thephotopolymerizable resin, the photopolymerizable resin described hereinalso contains one or more additional components comprising aminemoieties or amine synergists. These one or more additional componentscontaining amine moieties or amine synergists may be selected fromvarious materials that include amine moieties, including for example,photoinitiators containing amine moieties, hindered amine lightstabilizers (HALS), thermal polymerization inhibitors, amine acrylates,amine reaction accelerators, and combinations of one or more of theforegoing. These one or more additional components comprising aminemoieties are used in the photopolymerizable composition at aconcentration of between about 0.1 to about 10 percent by weight, morepreferably about 0.2 to about 5.0 percent by weight, based on the totalweight of the composition.

Suitable photoinitiators that contain amine moieties includeaminoacetophenone initiators, commercial products of which are availablefrom BASF under the tradenames IRGACURE® 907, IRGACURE® 369, andIrgacure® 379. Other aminoacetophenone initiators that can be usedinclude the compounds described in JP2009-191179 to Toyo InkManufacturing. One preferred photoinitiator is2-dimethylamine-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one(CAS #: 119344-86-4), available from BASF, under the tradename Irgacure®379.

Suitable hindered amine light stabilizers (HALS) include, for example,materials that contain 2,2,6,6-tetrametyl-4-piperidyl groups, includingmaterials such as those described in U.S. Pat. Pub. No. 20150252202 toNerad, the subject matter of which is herein incorporated by referencein its entirety. Preferred materials that contain2,2,6,6-tetrametyl-4-piperidyl groups include, for example,bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate (CAS #: 52829-07-9), acommercial product of which is available from BASF, under the tradenameTinuvin 770 and from Mayzo, Inc. under the tradename BLS 1770, as wellas other derivatives of 2,2,6,6-tetramethylpiperidine and derivatives of1,2,2,6,6-pentamethylpiperidine; dimethyl succinate polymer with4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol (CAS #: 65447-77-0),available from Mayzo, Inc., under the tradename BLS 1622;poly[[6-[(1,1,3,3,-tetramethylbutyl)amino-s-triazine-2,4-diyl][2,2,6,6-tetramethyl-4-piperidyl)imino]]hexamethyl-ylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]](CAS #: 70624-18-9), available from Mayzo, Inc. under the tradename BLS1944; andN,N′,N″,N′″-tetrakis(4,6-bis(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)triazin-2-yl)-4,7-diazadecane-1,10-diamine (CAS #: 106990-43-6),available from Mayzo, Inc. under the tradename BLS 119.

Suitable thermal polymerization inhibitors containing amine moietiesinclude aluminum N-nitroso-N-phenylhydroxylamine (CAS #: 15305-07-4),available from Shanghai Boer Chemical Reagent Co., Ltd. under thetradenamne BR510 and from Wako Pure Chemical Industries and a liquidblend of aluminum N-nitrosophenylhydroxylamine (CAS #15305-07-4) anddi-trimethylol-propane tetraacrylate (CAS #94108-97-1), available fromIGM Resins under the tradename Omnistab IN 522.

Suitable amine acrylates include, for example, hexane-1,6-diylbisprop-2-enoate-2-aminoethanol (CAS #: 67906-98-3), commercialsproducts of which are available from IGM Resins under the tradenamesPhotomer 4771 and Photomer 4775; and 2-Propenoic acid,(1-methyl-1,2-ethanediyl)bisoxy(methyl-2,1-ethanediyl) ester reactionproducts with diethylamine (CAS #: 111497-86-0), a commercial product ofwhich is available from IGM Resins under the tradename Photomer 4967.

Suitable amine reaction accelerators, include primary, secondary andtertiary aliphatic, aromatic, aliphatic or heterocyclic amines. Examplesof these amines include butylamine, dibutylamine, tributylamine,cyclohexyl amine, benzyldiniethylamine, dicyclohexylamine,triethanolamine, N-methyldiethanolamine, phenyldiethanolamine,piperidine, piperazine, morpholine, pyridine, quinoline, ethylp-dimethylaminobenzoate, butyl p-dimethylamino benzoate,4,4′-bis(dimethylamino)-benzophenone (Michler's ketone) and4,4′-bis(diethylamino)-benzophenone. Particularly preferred aminereaction accelerators include dibutylamine and triethanolamine.

In another embodiment, the present invention relates generally to amethod of producing a relief image printing element from a photocurableprinting blank, the method comprising the steps of:

-   -   a) providing a photocurable printing blank, the photocurable        printing blank comprising:        -   i) a backing or support layer;        -   ii) one or more photocurable layers disposed on the backing            or support layer, wherein the one or more photocurable            layers comprise:            -   1) a binder;            -   2) one or more monomers;            -   3) a photoinitiator;            -   4) an additive selected from the group consisting of                phosphites, phosphines, thioether amine compounds, and                combinations of one or more of the foregoing; and            -   5) an additional component comprising amine moieties;        -   iii) a laser ablatable masking layer disposed on the at            least one photocurable layer, the laser ablatable masking            layer comprising a radiation opaque material;    -   b) selectively ablating the laser ablatable mask laser to create        an in situ negative of a desired image in the laser ablatable        mask layer;    -   c) exposing the at least one photocurable layer to actinic        radiation through the in situ negative to selectively crosslink        and cure portions of the at least one photocurable layer; and    -   d) developing the exposed at least one photocurable layer of the        photocurable printing blank to reveal the relief image therein,        said relief image comprising a plurality of relief printing        dots.

The photocurable compositions can be developed using a solvent todissolve away the uncured and uncrosslinked portions of the photocurablecomposition or developed using thermal development in which the uncuredand uncrosslinked portions were softened and/or melted and then blottedaway. Other means of developing the photocurable composition are alsoknown to those skilled in the art.

The resulting photocured relief image printing element preferably has aShore A hardness of between about 45 and about 70, more preferablybetween about 50 and about 65.

Tables 1 and 2 summarize various examples of various formulae ofphotocurable compositions prepared in accordance with the presentinvention. These photocurable compositions were imagewise exposed toactinic radiation and developed to reveal the relief image thereincomprising a plurality of relief printing dots. The resulting photocuredcompositions comprising the plurality of relief printing dots were thenexamined.

TABLE 1 Various formulae prepared in accordance with the presentinvention (% by wt.) Component Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7Binder 64.39 64.39 63.89 64.59 64.39 64.39 64.39 Plasticizer 19.86 19.8619.86 19.86 19.36 19.36 19.36 Methacrylate 8.95 8.95 8.95 8.95 8.95 8.958.95 monomer Irgacure ® 651 5 5 5 3 5 5 5 TNPP 1.8 1.3 1.8 0.57 1.8 1.81.8 Solvaperm Red BB 0.0025 0.0025 0.0025 0.0025 0.0025 0.0025 0.0025TPP 0.93 BHT 0.50 0.10 Tinuvin 770 0.50 Irgacure 379 2.0 520 0.5 NPAL0.5 BLS 119 0.5 Total 100 100 100 100 100 100 100 Light Stability 5 1 11 3 3 4 Holding dots at 1%- Yes Yes No Yes Yes Yes Yes 200 lpi?

TABLE 2 Various formulae prepared in accordance with the presentinvention (% by wt.) Component Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13Ex. 14 Binder 64.39 64.39 64.39 64.39 64.39 64.39 64.39 Plasticizer19.36 19.36 16.39 16.39 16.39 19.36 19.36 Methacrylate monomer 8.95 8.958.95 8.95 8.95 8.95 8.95 Irgacure ® 651 5 5 5 5 5 5 5 TNPP 1.8 1.8 1.81.8 1.8 1.8 1.8 Solvaperm Red BB 0.0025 0.0025 0.0025 0.0025 0.00250.0025 0.0025 BLS 1622 0.5 BLS 1944 0.5 Photomer 4771 3.0 Photomer 47753.0 Photomer 4967 3.0 Dibutylamine 0.5 Triethanolamine 0.5 Total 100 100100 100 100 100 100 Light Stability 4 4 4 4 3 Holding dots at 1%-200 YesYes Yes Yes Yes lpi?

The holding dots at 1%-200 lpi was determined by reviewing SEM picturesof each Example.

Light stability of each formulation was determined by expediting lightexposure testing at 12 μW/cm² for seven days. The light stability wasquantified on a scale of 1 to 5, with 1 being the best and 5 being theworst.

Example 1 is a Comparative Example which contains a phosphite additivebut that does not contain an additional component containing aminemoieties. As seen in Table 1, while this Example does hold 1% dots at200 lpi, the light stability is very poor, as seen in FIG. 2, asformulation SPF841.

Example 3 is another Comparative Example which contains BHT as a thermalpolymerization inhibitor. As seen in Table 1, while the light stabilityis good in this example, the composition was not capable of holding 1%dots at 200 lpi, as seen in FIG. 2 as formulation SPF889.

Example 4 describes a composition in which 0.1 percent by weight of BHTwas added for thermal stability during extrusion of the photocurablecomposition in combination with Irgacure® 379 as the additionalcomponent containing amine moieties. As seen from this Example, both thelight stability and the ability to hold 1% dots at 200 lpi were good.

The results show that the light stability of the photocurablecomposition can be improved by the addition of a component containingamine moieties to the composition.

As described in U.S. Pat. No. 8,808,968, the improved surface cure inthe relief image printing elements can be revealed by the shape of thedots, and it is desirable that the dot shape exhibit a flat top.

The planarity of the top of a dot can be measured as the radius ofcurvature across the top surface of the dot, r_(e). It is noted that arounded dot surface is not ideal from a printing perspective because thesize of the contact patch between the print surface and the dot variesexponentially with impression force. Therefore, the top of the dotpreferably has a planarity where the radius of curvature of the dot topis greater than the thickness of the photopolymer layer, more preferablytwice the thickness of the photopolymer layer, and most preferably morethan three times the total thickness of the photopolymer layer.

Edge sharpness relates to the presence of a well-defined boundarybetween the planar dot top and the shoulder and it is generallypreferred that the dot edges be sharp and defined. These well-defineddot edges better separate the “printing” portion from the “support”portion of the dot, allowing for a more consistent contact area betweenthe dot and the substrate during printing,

Edge sharpness can be defined as the ratio of r_(e), the radius ofcurvature (at the intersection of the shoulder and the top of the dot)to p, the width of the dot's top or printing surface. For a trulyround-tipped dot, it is difficult to define the exact printing surfacebecause there is not really an edge in the commonly understood sense,and the ratio of r_(e):p can approach 50%, In contrast, a sharp-edgeddot would have a very small value of r_(e), and r_(e):p would approachzero. In practice, an r_(e):p of less than 5% is preferred, with anr_(e):p of less than 2% being most preferred.

Finally, it should also be understood that the following claims areintended to cover all of the generic and specific features of theinvention described herein and all statements of the scope of theinvention that as a matter of language might fall there between.

What is claimed is:
 1. A flexographic photocurable printing blankcomprising: a) a support layer; b) one or more photocurable layersdisposed on the support layer, wherein the one or more photocurablelayers comprise: i) a binder; ii) one or more monomers; iii) aphotoinitiator; iv) an additive selected from the group consisting ofphosphites, phosphines, thioether amine compounds, and combinations ofone or more of the foregoing; and v) an additional component comprisingamine moieties, wherein the additional component comprising aminemoieties is one or more components selected from the group consisting ofhindered amine light stabilizers selected from the group consisting ofbis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate, derivatives of2,2,6,6-tetramethylpiperidine, derivatives of1,2,2,6,6-pentamethylpiperidine; dimethyl succinate polymer with4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol,poly[[6-[(1,1,3,3,-tetramethylbutyl)amino-s-triazine-2,4-diyl][2,2,6,6-tetramethyl-4-piperidyl)imino]]hexamethyl-ylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]],N,N′,N″,N′″-tetrakis(4,6-bis(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)triazin-2-yl)-4,7-diazadecane-1,10-diamine, and combinations ofone or more of the foregoing, amine acrylates, and thermalpolymerization inhibitors selected from aluminumN-nitroso-N-phenylhydroxylamine, a liquid blend of aluminumN-nitrosophenylhydroxylamine and di-trimethylol-propane tetraacrylate,and combinations of the foregoing; c) a laser ablatable masking layerdisposed on the one or more photocurable layers, the laser ablatablemasking layer comprising a radiation opaque material; and d) optionally,a removable coversheet.
 2. The flexographic photocurable printing blankaccording to claim 1, wherein the additive comprisestris(nonylphenyl)phosphite.
 3. The flexographic photocurable printingblank according to claim 1, wherein the additive is a thioether aminecompound selected from the group consisting of2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol,4-[[4,6-bis(nonylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(octadecylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-octylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-bis(2-methylnonan-2-yl)phenol,4-[[4,6-bis(hexylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(heptylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl]amino]-2-tert-butyl-6-m-ethylphenol,4-[[4,6-bis(ethylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(2,4,4-trimethylpentan-2-ylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(2-octylsulfanylethylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-ditert-butylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-dibutylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-dimethylphenol,2,6-ditert-butyl-4-[[4-(3,5-ditert-butyl-4-hydroxyanilino)-6-octylsulfany-1-1,3,5-triazin-2-yl]amino]phenol,4-[[4,6-bis(pentylsulfanyl)-1,3,5-triazin-2-yl]amino-2,6-dimethylphenol,4-[[4,6-bis(hexylsulfanyl)-1,3,5-triazin-2-yl]amino]-2-tert-butylphenol,2,6-ditert-butyl-4-[(4-octylsulfanyl-1,3,5-triazin-2-yl)amino]phenol,4-[[4,6-bis(ethylsulfanyl)-1,3,5-triazin-2-yl]amino]-2,6-dimethylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl]-butylamino]-2,6-ditert-butylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl]-cyclohexylamino]-2,6-ditert-butylphenol,2-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl]amino]-6-tert-butylphenol,2-tert-butyl-6-methyl-4-[[4-octylsulfanyl-6-[(2,2,6,6,-tetramethylpiperidin-4-yl)amino]-1,3,5-triazin-2-yl]amino]phenol,4-[[4,6-bis(octylsulfanylmethyl)-1,3,5-triazin-2-yl)amino]-2,6-ditert-butylphenol,4-[[4,6-bis(octylsulfanyl)-1,3,5-triazin-2-yl)methylamino]-2,6-ditert-butylphenol,4-[(4-amino-6-chloro-1,3,5-triazin-2-yl)amino]-2,6-ditert-butylphenol,and4-[(4-cyclohexyl-6-cyclohexylsulfanyl-1,3,5-triazin-2-yl)amino]-2,6-di(propan-2-yl)phenol.4. The flexographic photocurable printing blank according to claim 3,wherein the additive comprises2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol.5. The flexographic photocurable printing blank according to claim 1,wherein the additive is a phosphine selected from the group consistingof triphenyl phosphine, tri-p-tolylphosphine, diphenylmethylphosphine,diphenylethylphosphine, diphenylpropylphosphine,dimethylphenylphosphine, diethylphenylphosphine,dipropylphenylphosphine, divinylphenylphosphine,divinyl-p-methoxyphenylphosphine, divinyl-p-bromophenylphosphine,divinyl-p-tolylphosphine, diallylphenylphosphine,divinyl-p-bromophenylphosphine, and diallyl-p-tolylphosphine andcombinations of one or more of the foregoing.
 6. The flexographicphotocurable printing blank according to claim 1, wherein the additionalcomponent containing amine moieties comprises the thermal polymerizationinhibitor selected from the group consisting of aluminumN-nitroso-N-phenylhydroxylamine, a liquid blend of aluminumN-nitrosophenylhydroxylamine and di-trimethylol-propane tetraacrylate,and combinations of the foregoing.
 7. The flexographic photocurableprinting blank according to claim 1, wherein the additional componentcontaining amine moieties comprises an amine acrylate selected from thegroup consisting of hexane-1,6-diyl bisprop-2-enoate-2-aminoethanol,2-Propenoic acid, (1-methyl-1,2-ethanediyl)bisoxy(methyl-2,1-ethanediyl)ester reaction products with diethylamine, and combinations of theforegoing.
 8. The flexographic photocurable printing blank according toclaim 1, wherein the additional component containing amine moieties ispresent in the one or more photocurable layers in an amount of between0.1 to 10 percent by weight, based on the total weight of thephotocurable composition.
 9. The flexographic photocurable printingblank according to claim 1, wherein the one or more photocurable layersfurther comprises one or more materials selected from the groupconsisting of plasticizers, antiozonants, fillers, reinforcing agents,thermal polymerization inhibitors, UV absorbers and combinations of oneor more of the foregoing.
 10. The flexographic photocurable printingblank according to claim 1, wherein the one or more photocurable layersdoes not contain butylated hydroxytoluene,2,4-Bis(octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine,or 1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene.11. The flexographic photocurable printing blank according to claim 9,wherein the one or more materials comprise a plasticizer.
 12. A methodof producing a flexographic relief image printing element from aflexographic photocurable printing blank, the method comprising thesteps of: a) providing a photocurable printing blank, the photocurableprinting blank comprising: i) a backing or support layer; ii) one ormore photocurable layers disposed on the backing or support layer,wherein the one or more photocurable layers comprise: 1) a binder; 2)one or more monomers; 3) a photoinitiator; 4) an additive selected fromthe group consisting of phosphites, phosphines, thioether aminecompounds, and combinations of one or more of the foregoing; and 5) anadditional component comprising amine moieties, wherein the additionalcomponent comprising amine moieties is one or more components selectedfrom the group consisting of hindered amine light stabilizers selectedfrom the group consisting ofbis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate, derivatives of2,2,6,6-tetramethylpiperidine, derivatives of1,2,2,6,6-pentamethylpiperidine; dimethyl succinate polymer with4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol,poly[[6-[1,1,3,3,-tetramethylbutyl)aminos-triazine-2,4-diyl][2,2,6,6-tetramethyl-4-piperidyl)imino]]hexamethyl-ylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]],N,N′,N″,N′″-tetrakis(4,6-bis(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)triazin-2-yl)-4,7-diazadecane-1,10-diamine, and combinations ofone or more of the foregoing, amine acrylates, and thermalpolymerization inhibitors selected from aluminumN-nitroso-N-phenylhydroxylamine, a liquid blend of aluminumN-nitrosophenylhydroxylamine and di-trimethylol-propane tetraacrylate,and combinations of the foregoing; iii) a laser ablatable masking layerdisposed on the one or more photocurable layers, the laser ablatablemasking layer comprising a radiation opaque material; b) selectivelyablating the laser ablatable mask laser to create an in situ negative ofa desired image in the laser ablatable mask layer; c) exposing the atleast one photocurable layer to actinic radiation through the in situnegative to selectively crosslink and cure portions of the one or morephotocurable layers; and d) developing the exposed one ox morephotocurable layers of the photocurable printing blank to reveal therelief image therein, said relief image comprising a plurality of reliefprinting dots.
 13. The method according to claim 12, wherein the reliefimage printing element does not degrade if left under ambient UV lightsfor an extended period of time.